The present invention concerns a method of checking a blending plant for textile staple fibres of different types, in which each type is supplied by a fibre metering unit each to a blending device and in which the fibres blended therein are supplied to a storage device, and in which during the supply times the fibre quantity supplied to the storage device is somewhat greater than the fibre quantity taken off from this storage device, and as a consequence the fibre supply to the storage device is interrupted during repeated time intervals, the metering units during such time intervals delivering fibres individually and consecutively, which fibres are used for checking the fibre quantity supplied by the metering units during the normal blending operation.
Plants operating according to such a method are known in practical spinning mill use. They are used for fibre blends composed of fibres of different types or kinds. A blend e.g. of natural and man-made fibres, or fibres of different colours or different qualities can be processed. It is important in this process that the fibre blends as well as yarns or twisted threads processed therefrom are uniform. The fibres delivered from the blending plant, or tufts are to represent a blending proportion, which is within sharply defined tolerance limits. If e.g. a base material for the production of clothing articles is processed, deviations from the tolerance limits can present a breach of legal requirements.
The checking methods already known, in which the checking is effected during the time intervals, during which the fibre supply to the storage device or to the reserve chute is interrupted, show as a disadvantage of relatively great imprecision. The cause for this is seen in that the fibre quantity supplied by an individually operating metering unit during the start-up and running-out phases of the supply deviates considerably from the fibre quantity supplied during normal operation at constant values. If the imprecision caused by these deviations are to be eliminated, the disadvantage of a prolonged measuring time is to be incurred. Thus, more fibre material is to be used for the measuring operation, and the measurements can be effected less frequently. Thus the checking operation is of reduced quality and becomes more expensive.
In such cases, in which only one check is effected per working shift, the individually operated metering unit can be running during a relatively long period of time, in such a manner that the deviations from the fibre quantity of constant value occurring during the start-up and running-out phases no longer are of substantial influence. In this case, however, a standstill period of the machine arranged subsequent to the blending plant during the checking operation is to be incurred.